1. Field of the Invention
The present invention relates to a laser machining apparatus.
2. Description of Related Art
A laser machining apparatus generally uses a numerical control apparatus as its controller. Such numerical control apparatus for laser machining apparatus outputs a motion command at intervals of a predetermined interpolation period, to thereby move a workpiece to be machined relative to a laser head, thus performing laser beam machining. Laser output, etc. of a laser oscillator are also often on/off controlled in units of the interpolation period.
If the machining speed is not high, no substantial problem is caused so that the required machining accuracy may be attained, even when the laser output of the laser oscillator is on/off controlled in units of the interpolation period that is intended to be used for control of the numerical control apparatus. At a higher machining speed, however, it is difficult to start or finish the laser machining at intended positions with high accuracy, without the laser oscillator being controlled in the course of the interpolation period.
Motion commands of the current and next blocks in an NC machining program that is input to the numerical control apparatus are sometimes required to be executed such that a command speed is maintained unchanged between these blocks. If a remaining motion amount of the current block (the distance to go) is less than a motion amount corresponding to the command speed for one distribution period, such deficiency is supplemented by block overlap processing to add part of a motion amount for the next block to the remaining motion amount for the current block, thus obtaining the motion command for the distribution period between these blocks which is capable of maintaining the moving speed unchanged. During the block overlap processing, the movement corresponding to the motion command for one block comes to end in the course of the interpolation period, but the laser output of the laser oscillator that is on/off controlled in units of the interpolation period cannot be turned on or off at the end of the one block, i.e., between two successive blocks.
In this regard, there has been proposed to determine a current position on the basis of speed command data output from the numerical control apparatus, position data fed back from the servo control system, and a time period measured from the start of the interpolation period, and to output a machining start signal when it is determined based on the determined position that a target position is reached (see, JP-A-9-258812).
When the on/off control of the laser oscillator is performed in synchronism with the interpolation period, the on/off timing is delayed with increase in machining speed at the maximum for a period of time corresponding to the interpolation period length, resulting in inaccurate machining. Such delay can be decreased by shortening the interpolation period length so as to improve the machining accuracy, however, the shortening of the interpolation period length for speedup results in increased costs.
With the invention disclosed in JP-A-9-258812 to predict, based on the position data fed back from the servo control system, when the machining start/end position will be reached, the accuracy of machining start/end position can be improved irrespective of the interpolation period length. On the other hand, this technical art poses a problem that overall operational processing becomes complicated since the feedback position data signal must be reprocessed and additional processing must be made to compensate for a change in machining speed.